Yarrow essential oil is a volatile oil including the chemical proazulene. The dark blue essential oil is extracted by steam distillation of the flowers of yarrow (Achillea millefolium).
^Conti B., Canale A., Bertoli A., Gozzini F., Pistelli L. (2010). "Essential oil composition and larvicidal activity of six Mediterranean aromatic plants against the mosquito Aedes albopictus (Diptera: Culicidae)". Parasitology Research. 107 (6): 1455–1461. doi:10.1007/s00436-010-2018-4. PMID20697909. S2CID20445073.((cite journal)): CS1 maint: multiple names: authors list (link)